1. Field of the Invention
The present invention relates to an organic/inorganic hybrid hydrogel, a dry gel body thereof, and a manufacturing methods therefor. The organic/inorganic hybrid hydrogel constituted by three constituents including a water soluble polymer, a water swelling clay mineral which can be homogeneously dispersed in water, and water, has a structure in which water is included in a three-dimensional network formed by the water soluble polymer and the water swelling clay mineral.
2. Description of the Related Art
A gel is a state of matter which is intermediate between solids and liquids, and which consists of a solvent inside a three dimensional network. Gels containing water (hereinafter, referred to as hydrogels or aqueous gels) are important material for living organisms and such hydrogels are used not only in the fields of the pharmaceuticals, medical care, foods, packaging, sanitary goods, and cosmetics, but also in the industrial fields of agriculture, civil engineering, and other industrial fields. (The fields of application of hydrogel products are described in detail in “Gel Handbook” authored by Yoshihisa Nagata and Kanji Kajiwara, published in 1997 by NTS Company).
Hydrogels include at least two constituents, water and a three dimensional network formed by various types of crosslinking. The three-dimensional network can be formed either by organic or inorganic compounds. In a hydrogel constituted by organic polymers, polymers or organic molecules are crosslinked by covalent bonds, hydrogen bonds, ionic bonds, and hydrophobic bonds, and the crosslinking can also be generated by physical entanglement or at crosslinking points of crystallites.
Known examples of organic molecules which form three dimensional networks includes albumen albumin, blood serum albumin, gelatin which forms networks by helix formation, polyacrylate or polystyrene sulfonic acid, which form bridges by coordinate bonds with agarose or alkaline earth metal ions, a two polymer-type (poly cation and poly anion) complex system, fully saponified polyvinyl alcohol which is bridged by hydrogen bonds, and the organic compounds formed by crosslinking polymers by forming covalent bonds therebetween by heat, radiation, light, or plasma, or by addition of an organic cross linking agent.
Examples of inorganic compounds which form three-dimensional networks include metal oxides prepared by hydrolysis polycondensation of the metal alkoxides and layered clay minerals containing cations between layers. Inorganic gels composed of inorganic materials and water are formed from these inorganic compounds forming three-dimensional networks by aggregation of fine particles owing to their interactions.
Hydrogels made of inorganic materials are brittle and have low strength and elongation, and as a result, they are not generally used alone as hydrogel materials. In contrast, since hydrogels made of organic materials, particularly hydrogels composed of water and three-dimensional network of polymers formed by covalent bonds, have superior mechanical properties to inorganic gels, the application of these organic gels is under development in a wide range of industrial fields such as soft materials or functional materials.
In order to expand availability of the organic hydrogels, the provision of new types of organic hydrogels, which further exhibit the superior properties of the organic compounds in a more effective manner, is being investigated to improve homogeneity, transparency, dynamic and mechanical properties, and absorption (water absorption) properties of these gels.
In the electrophoresis, which has been widely used in the fields of chemistry, biochemistry, and medical care, filter paper, which has been used in the past as the electrophoresis medium (membrane), has recently been replaced with a polyacrylamide type hydrogel (hydrogel membrane obtained by crosslinking the polyacrylamide-type polymer using a polymer cross linker) due to its high performance. However, this hydrogel membrane has drawbacks in its characteristics such as low flexibility and fragileness due to its brittleness. In order to reduce the brittleness of the polymer gel membrane, a few measures have been proposed, one of which is to add agarose to the gel membrane (Japanese Patent (Granted) Publication No. Hei 4-77264) and the other one is to add a tri-functional organic cross linker (Japanese Patent Granted Publication No. Hei 4-77868). However, a further improvement in the toughness of the membrane is required.
In aqueous solution absorbent materials used for absorbing aqueous solutions such as physiological products, paper diapers, or other absorbent materials for absorbing body fluids, hydrogels with further improved absorptive properties and the mechanical characteristics of a gel are still required due to continuing advances of social activities of women and the aging of society. Although a few measures has been proposed, one of which is to bridge the surfaces of pulverized absorbing polymers using a cross linker (Japanese Patent (Granted) Publication Nos. Sho 60-18690, Sho61-48521, Hei 6-39487, Hei 6-74331, and U.S. Pat. No. 5,314,420), and another of which is to use trimethylolpropane triacrylate as the cross linker (WO 94/20547), further improvements in the absorbing property and the strength of the hydrogel remain necessary.